The drawn and ironed two piece beverage container is a highly engineered article of manufacture. However, improvements are constantly being sought that will permit reliable containers to be made with less metal. Due to the extremely high volume in which such containers are manufactured, even the smallest savings in the metal from which they are made can result in enormous cost reductions. For example, it would be desirable to reduce the starting gauge of such containers by as little as one one-tenthousandth (0.0001) of an inch.
One of the fundamental operations required to form a two piece beverage container is the drawing, redrawing and wall ironing of a thin sheet of metal into a deep cup that essentially forms the body of the container, i.e., the portion that holds the liquid. Although the bulk of the drawn and ironed containers presently manufactured are formed of aluminum or aluminum alloys, other metals, such as steel are also drawn and redrawn using substantially the same techniques.
U.S. Pat. No. 4,425,778--Franek et al. discloses methods and apparatus for redrawing a can body by pulling the side wall through an S-shaped path by bending the side wall of the cup that is being redrawn around a redraw ring to induce tensions to stretch the metal and reduce the wall thickness that can be redrawn without wrinkles.
U.S. Pat. No. 4,685,322--Clowes discloses a redrawing die that has an inwardly projecting annular bead formed on the redraw ring to prevent wrinkling in the end wall of a container as it is redrawn.
U.S. Pat. No. 4,962,659--Inazu et al. discloses apparatus for redrawing a drawn cup by relatively moving a redrawing die in a redrawing punch wherein the redrawing die and punch comprise portions that engage one another to clamp the cup and permit a redrawn cup of a relatively thin wall to be reformed.
U.S. Pat. No. 5,083,449--Kobayashi et al. discloses apparatus for redrawing a flanged cup using a redraw ring that has a working face having an inner diameter which is gradually decreased and a peripheral portion that clamps the flanged cup to the redraw ring.
However, it has been found that using the methods and apparatus of the prior art, as the gauge of the metal is reduced, wrinkling occurs in the unsupported nose portion of the container as the cup is redrawn. For this reason, a wrinkle-free redrawn cup cannot be produced when the thickness of the base metal is below 0.0113 inches using the technology currently available. Radial faults develop in the area of the cup face that is not directly clamped nor in contact with the punch. This phenomenon is thought to be due to insufficient holding force being developed between the bottom of the cup, the face of the redraw ring, and the corresponding face of any clamping means associated with it. It would be desirable to provide methods and apparatus whereby thinner gauge metals could be redrawn to produce lightweight container bodies. Therefore, it is an object of the present invention to provide methods and apparatus for increasing the clamping force during a redraw operation such that the wrinkling of the unsupported nose portion is eliminated.